Measurements of gravity can be made from aircraft, and are routinely used in some resource exploration particularly petroleum exploration. A measurement of gravity gradient is preferred for detection of gravity disturbances from an airborne platform because the direct measurement of gravity cannot distinguish the gravity signal from accelerations of the instrument associated with the motion of the aircraft. This is particularly important at low altitude surveying preferred in mineral exploration to improve spatial resolution of the survey, because of the prevalence of atmospheric turbulence close to the ground surface. An ideal gravity gradient measurement will not be sensitive to the motion of the instrument.
The principal source of measurement noise (error) is residual sensitivity of the GGI to motion. The magnitude of gravity gradient signal expected from an economic mineral deposit is in the range 1-100 Eotvos 1 Eotvos=10.sup.-9 (m/s.sup.2)/m!. Accelerations experienced in a survey aircraft during low level surveys are generally of the order of 1-10 m/s.sup.2 and the GGI has a baseline length of 0.1 to 0.4 m. The acceleration rejection of the GGI therefore must be of the order of one part in 10.sup.9.